JP7854108B2 - Optical styrene resin composition, molded body, light guide plate, and edge-lit surface light source unit - Google Patents

Description

The present invention relates to an optical styrene-based resin composition, a molded article, a light guide plate, and an edge-lit surface light source unit.

Liquid crystal display (LCD) backlights come in two types: direct-lit backlights, where the light source is located in front of the display, and edge-lit backlights, where the light source is located on the side. Edge-lit backlights use a component called a light guide plate, which directs the light from the side-mounted light source to the front of the display. They are used in a wide range of applications, including televisions, desktop computer monitors, notebook computers, mobile phones, and car navigation monitors. Backlights using light guide plates are also used in lighting fixtures and signs.

Light guide plates require particularly high light transmittance because they have a relatively long light transmission distance and significant light loss along the optical path. For this reason, acrylic resins, such as polymethyl methacrylate (PMMA), are commonly used as materials for light guide plates. However, PMMA has high water absorption, which can cause warping and dimensional changes in the light guide plate. Furthermore, because it is easily thermally decomposed during molding, molding at high temperatures can easily result in surface defects in the molded product. To improve these problems, for example, Patent Document 1 proposes using styrene-(meth)acrylate copolymer as a material for light guide plates.

On the other hand, molded articles of styrene-(meth)acrylate copolymer have poorer hue compared to PMMA, and when used as backlights, color unevenness may occur. To improve this problem, Patent Document 2 proposes a technique for improving the hue of styrene-(meth)acrylate.

Japanese Patent Publication No. 2003-075648 International Publication No. 2016/129675

In recent years, with the increasing resolution of backlight units in televisions and monitors, high-brightness LEDs are sometimes used as edge light sources. However, conventional styrene-(meth)acrylate copolymer light guide plates could deteriorate (yellowing) at their edges after prolonged illumination, depending on the usage environment. Furthermore, in recent years, displays using mini-LEDs with higher energy blue light as the light source and performing color conversion with QDs (quantum dots) have emerged, requiring increasingly sophisticated light stability from light guide plates.

This invention has been made in view of the above problems, and provides an optical styrene-based resin composition that exhibits excellent light stability for long-term use of semiconductor light sources such as LED light sources.

As a result of diligent research to solve the above problems, the inventors of the present invention have found that the above problems can be solved by setting the content of styrene monomers, the content of styrene monomer linear dimers, and the content of styrene monomer linear trimers in the styrene resin composition within a predetermined range, and have completed the present invention.

The following inventions are provided.
[1] A styrene-based resin composition for optical use containing a styrene-based resin,
Per 1 g of the aforementioned optical styrene-based resin composition,
The styrene monomer content is 1000 μg or less.
The total content of styrene monomer linear dimers and styrene monomer linear trimers is 10 to 500 μg.
A styrene-based resin composition for optical applications.
[2] The styrene resin is a copolymer comprising 95 to 20% by mass of styrene monomer units and 5 to 80% by mass of (meth)acrylic acid ester monomer units, as described in [1].
[3] The optical styrene-based resin composition according to [1] or [2], wherein the phosphorus atom content is 50 μg or less per 1 g of the optical styrene-based resin composition.
[4] When the content of the styrene monomer is Mμg, the content of the styrene monomer linear dimer is Dμg, the content of the styrene monomer linear trimer is Tμg, and the content of the phosphorus atom is Pμg per 1g of the optical styrene resin composition,
An optical styrene-based resin composition according to any one of [1] to [3] that satisfies the following formula (1).
(M+D+T)×P≦20000(1)
[5] The optical styrene resin composition according to any one of [1] to [4], comprising 0.001 to 0.5 parts by mass of a hindered amine light stabilizer per 100 parts by mass of the styrene resin.
[6] An optical styrene-based resin composition according to any one of [1] to [5], for use in transmitting light from an LED light source having maximum radiant intensity in the wavelength range of 400 nm to 500 nm.
A molded article comprising an optical styrene-based resin composition as described in any one of [7], [1], to [6].
A light guide plate comprising the molded bodies of [8] and [7].
An edge-lit surface light source unit having a light guide plate as described in [9] and [8], and a light source that supplies LED light to the end face of the light guide plate.

Figure 1 is a diagram illustrating the shape of the plate-shaped test specimen 1.

The embodiments of the present invention will now be described. The various features shown in the embodiments below can be combined with each other. Furthermore, each feature constitutes an independent invention.

1. Styrene resin composition for optical applications The styrene resin composition for optical applications according to one embodiment of the present invention comprises a styrene resin (A).
<Styrene resin (A)>
Styrene-based resin (A) is a resin obtained by polymerizing raw material monomers containing styrene monomers. Styrene-based resin (A) is preferably a resin obtained by copolymerizing a monomer containing styrene monomers and (meth)acrylic acid ester monomers. Styrene-based resin (A) is preferably a copolymer (styrene-acrylic acid ester copolymer) containing styrene monomer units and (meth)acrylic acid ester monomer units. The styrene-acrylic acid ester copolymer contains 95 to 20% by mass of styrene monomer units and 5 to 80% by mass of (meth)acrylic acid ester monomer units in 100% by mass of the styrene-acrylic acid ester copolymer. Preferably, it contains 90 to 25% by mass of styrene monomer units and 10 to 75% by mass of (meth)acrylic acid ester monomer units. More preferably, it contains 80 to 30% by mass of styrene monomer units and 20 to 70% by mass of (meth)acrylic acid ester monomer units. Even more preferably, it contains 60 to 40% by mass of styrene monomer units and 40 to 60% by mass of (meth)acrylic acid ester monomer units. By setting the copolymer within these ranges, transparency, hue, and dimensional stability can be simultaneously satisfied. By setting the styrene monomer content to 90% by mass or less, a molded article (such as a light guide plate) with excellent transparency and hue can be obtained, and by setting the styrene monomer content to 20% or more, a molded article with excellent dimensional stability can be obtained. The content of (meth)acrylic acid ester monomer units in the styrene resin (A) is specifically, for example, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, and 80% by mass, and may be within the range of any two of the values exemplified here.

Examples of styrene monomers include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, ethylstyrene, and p-t-butylstyrene. These can be used individually or in combination of two or more. The styrene monomer is preferably styrene.

Examples of (meth)acrylate monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isoamyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; and alkyl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate. Examples include cycloalkyl esters of (meth)acrylates such as cyclohexyl (meth)acrylate, 4-t-butylcyclohexyl (meth)acrylate, 2-norbornyl (meth)acrylate, isobornyl (meth)acrylate, adamantan-1-yl (meth)acrylate, 2-methyladamantan-2-yl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, and tricyclodecanyl (meth)acrylate; glycidyl (meth)acrylate; and dicyclopentanyl (meth)acrylate. These can be used individually or in combination of two or more. The (meth)acrylate ester monomer is preferably an alkyl (meth)acrylate, and more preferably methyl methacrylate.

Furthermore, the styrene-based resin (A) may be a copolymer obtained by copolymerizing a styrene-based monomer and another monomer copolymerizable with the (meth)acrylic acid ester monomer. Examples of other copolymerizable monomers include (meth)acrylic acids such as acrylic acid and methacrylic acid; vinyl cyanides such as acrylonitrile and methacrylonitrile; α,β-ethylene unsaturated carboxylic acids such as maleic anhydride and fumaric acid; and imides such as phenylmaleimide and cyclohexylmaleimide. These can be used individually or in combination of two or more.

The weight-average molecular weight (Mw) of the styrene-based resin (A) is preferably 50,000 to 400,000, and more preferably 100,000 to 350,000. Furthermore, the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) (Mw/Mn) of the styrene-based resin (A) is preferably 3.5 or less, more preferably 1.0 to 3.5, and even more preferably 1.5 to 3.0. By setting the ratio within this range, both moldability and the strength of the light guide plate can be achieved. If the weight-average molecular weight (Mw) is less than 50,000, the strength of the molded product will be insufficient, and if it exceeds 400,000, the moldability may decrease. Also, if the ratio of the number-average molecular weight (Mn) (Mw/Mn) exceeds 3.5, the strength of the molded product may decrease.

<Hindered amine light stabilizer>
The optical styrene resin composition preferably contains 0.001 to 1.0 parts by mass of hindered amine light stabilizer (B) per 100 parts by mass of styrene resin (A), more preferably 0.001 to 0.5 parts by mass, and even more preferably 0.05 to 0.3 parts by mass. By setting the content within this range, the light stability can be improved. Specifically, the content of hindered amine light stabilizer (B) relative to styrene resin (A) is, for example, 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 parts by mass, and may be within the range of any two of the values exemplified here. Furthermore, the hindered amine light stabilizer (B) may be used alone or in combination of two or more types.

Hindered amine light stabilizers (B) are compounds having a structural unit represented by the following general formula (1).

In general formula (1), X is an organic group bonded to the 4-position of the piperidyl group via a carbon atom, oxygen atom, or nitrogen atom, and R can be a hydrogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, a methylene group, or an alkoxy group. Here, when R is a hydrogen atom, it is called an N-H type hindered amine light stabilizer; when R is a linear or branched alkyl group having 1 to 10 carbon atoms or a methylene group, it is called an N-R type hindered amine light stabilizer; and when R is an alkoxy group, it is called an N-OR type hindered amine light stabilizer.

Specific examples of N-H type hindered amine light stabilizers include bis(2,2,6,6-tetramethylpiperidine-4-yl) sebacate (BASF TINUVIN770DF), 2,2,6,6-tetramethyl-4-piperidyl hexadecanoate, 2,2,6,6-tetramethyl-4-piperidyl octadecanoate (SONGWON SABOSTAB UV91), and tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate (ADEKA ADK STAB). Polycondensate of N,N'-bis(2,2,6,6-tetramethylpiperidine-4-yl)hexamethylenediamine and 4-morpholino-2,6-dichloro-1,3,5-triazine (SABOSTAB UV79, manufactured by SONGWON), polycondensate of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine/N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine (manufactured by BASF) Chimassorb 944FDL), polycondensate of N,N'-bis(2,2,6,6-tetramethylpiperidine-4-yl)hexamethylenediamine, 2,4,6-trichloro-1,3,5-triazine, N-butyl-1-butanamine, and N-butyl-2,2,6,6-tetramethyl-4-piperidineamine (Sangwon, Inc., SABOSTAB UV40), 1,6,11-tris[2,4-bis(N-butyl-N-(2,2,6,6-tetramethyl-4-piperidyl)amino)-s-triazine-6-yl]aminoundecane (BASF, Inc.) Chimassorb2020FDL), polycondensate of 1,2,3,4-butanetetracarboxylic acid, 2,2,6,6-tetramethyl-4-piperidinol, and β,β,β′,β′-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undencan-3,9-diethanol (ADKSTAB LA-68, manufactured by ADEKA Corporation), dodecyl 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro(5.1.11.2)henicosan-20-yl)propionate, tetradecyl Examples include 3-(2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro(5.1.11.2)henicosan-20-yl)propionate (HOSTAVIN 3030, manufactured by CLARIANT) and a polycondensate of 2,2,4,4-tetramethyl-7-oxa-3,20-diazadispiro(5.1.11.2)henicosan-21-one and epichlorohydrin (HOSTAVIN N30P, manufactured by CLARIANT).

Specific examples of N-R type hindered amine light stabilizers include methyl(1,2,2,6,6-pentamethylpiperidine-4-yl) sebacate, bis(1,2,2,6,6-pentamethylpiperidine-4-yl) sebacate (BASF TINUVIN 292, TINUVIN 765), bis(1,2,2,6,6-pentamethylpiperidine-4-yl) n-butyl 3,5-di-tert-butyl 4-hydroxybenzylmalonate (BASF TINUVIN 144), and polycondensate of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol and dimethyl succinate (BASF Tinuvin 622SF), 1,5,8,12-Tetrakis[4,6-bis(N-butyl-N-(1,2,2,6,6-pentamethyl-4-piperidyl)amino)-1,3,5-triazine-2-yl]-1,5,8,12-tetraazadodecane (BASF Chimassorb 119), polycondensate of 1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinol, and β,β,β',β'-tetramethyl-2,4,8,10-tetraoxaspiro[5,5]undencan-3,9-diethanol (ADEKA ADKSTAB) Examples include LA-63P), a polycondensate of succinic acid and (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-yl)ethanol, and a mixture of N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidine-4-yl)amino)-triazine-2-yl)-4,7-diazadecane-1,10-diamine (TINUVIN111FDL, manufactured by BASF).

Specific examples of N-OR type hindered amine light stabilizers include bis(1-octyloxy-2,2,6,6-tetramethylpiperidyl) sebacate (BASF TINUVIN 123) and bis(1-undecanoxy-2,2,6,6-tetramethylpiperidine-4-yl) carbonate (ADEKA ADKSTAB LA-81).

<Antioxidant (C)>
The optical styrene resin composition preferably contains 0.001 to 0.5 parts by mass of a phosphorus-based antioxidant (C-1) per 100 parts by mass of styrene resin (A), more preferably 0.002 to 0.4 parts by mass, and even more preferably 0.005 to 0.3 parts by mass. By using this range, good transparency and hue can be obtained. The content of the phosphorus-based antioxidant (C-1) is, specifically, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or 0.5 parts by mass per 100 parts by mass of the styrene-based resin (A), and may be within the range of any two of the values exemplified here.

Phosphorus-based antioxidants (C-1) are ()phosphorus esters that do not have a phenolic hydroxyl group in their basic skeleton, and are preferably trivalent phosphorus compounds. Specific examples of phosphorus-based antioxidants (C-1) include 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, bis-(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl)phosphite, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, tetrakis(2,4-di-tert-butylphenyl)[1,1-biphenyl]-4,4'-diylbisphosphonite, bis(2,4-di-tert-butyl-6-methylphenyl)ethyl phosphate, etc., and these can be used individually or in combination of two or more.

Furthermore, the optical styrene resin composition preferably contains 0.001 to 0.5 parts by mass of a phenolic antioxidant (C-2) per 100 parts by mass of styrene resin (A), more preferably 0.002 to 0.4 parts by mass, and even more preferably 0.005 to 0.3 parts by mass. A content of phenolic antioxidant (C-2) exceeding 0.5 parts by mass is undesirable because it deteriorates the hue. The content of the phenolic antioxidant (C-2) is, specifically, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, or 0.5 parts by mass per 100 parts by mass of the styrene resin (A), and may be within the range of any two of the values exemplified here.

Phenolic antioxidants (C-2) are antioxidants that have a phenolic hydroxyl group in their basic structure and are not (phosphorus) esters. Specific examples of phenolic antioxidants (C-2) include octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, ethylenebis(oxyethylene)bis[3-(5-tert-butyl-4-hydroxy-m-tolyl)propionate], and pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. These can be used individually or in combination of two or more.

Antioxidants include phosphorus-phenol compounds that possess both phosphite and phenol structures within the same molecule, such as 6-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-tert-butyldibenzo[d,f][1,3,2]dioxaphosfepine. In the case of such compounds, it is assumed that the optical styrene resin composition contains both a phosphorus-based antioxidant and a phenol-based antioxidant. For example, if 0.1 parts by mass of a phosphorus-phenol compound is contained per 100 parts by mass of styrene resin (A), it is assumed that 0.1 parts by mass of the phosphorus-based antioxidant and 0.1 parts by mass of the phenol-based antioxidant are contained.

<Monomers, dimers, trimers, and phosphorus>
In the optical styrene resin composition, the content of styrene monomers per 1 g of the optical styrene resin composition is 1000 μg or less, preferably 700 μg or less, and more preferably 500 μg or less. The lower limit of the styrene monomer content is not particularly limited, but for example, it is 1 μg or more. Specifically, the content of styrene monomers per 1 g of the optical styrene resin composition may be, for example, 0, 1, 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 μg, and may be within the range of any two of the values exemplified here. By setting the content within this range, the optical styrene resin composition exhibits excellent light stability.

In the optical styrene resin composition, the total content of styrene monomer linear dimers and styrene monomer linear trimers (D+T) per 1 g of the optical styrene resin composition is 10 to 500 μg, preferably 400 μg or less, and more preferably 300 μg or less. Specifically, the total (D+T) per 1 g of the optical styrene resin composition is, for example, 10, 50, 100, 150, 200, 250, 300, 330, 350, 400, 420, 450, and 500 μg, and may be within the range of any two of the values exemplified here. By setting it within this range, the optical styrene resin composition exhibits excellent light stability.

In the optical styrene resin composition, the content of styrene monomer linear dimers per 1 g of the optical styrene resin composition is preferably 500 μg or less, preferably 100 μg or less, and more preferably 50 μg or less. The lower limit of the content of styrene monomer linear dimers per 1 g of the optical styrene resin composition is not particularly limited, but for example, it is 1 μg or more. Specifically, the content of styrene monomer linear dimers per 1 g of the optical styrene resin composition is, for example, 0, 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500 μg, and may be within the range of any two of the values exemplified here. By setting the content within this range, the optical styrene resin composition exhibits excellent light stability.

In the optical styrene-based resin composition, the content of styrene monomer linear trimers per 1 g of the optical styrene-based resin composition is preferably 500 μg or less, preferably 300 μg or less, and more preferably 200 μg or less. The lower limit of the content of styrene monomer linear trimers per 1 g of the optical styrene-based resin composition is not particularly limited, but is, for example, 10 μg or more. The content of styrene monomer linear trimers per 1 g of optical styrene resin composition is specifically, for example, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 350, 400, and 500 μg, and may be within the range of any two of the values exemplified here. By setting the content within this range, the optical styrene resin composition exhibits excellent light stability.

In the optical styrene resin composition, the phosphorus atom content is preferably 100 μg or less, more preferably 50 μg or less, and even more preferably 20 μg or less per gram of the optical styrene resin composition. The lower limit of the phosphorus atom content per gram of the optical styrene resin composition is not particularly limited, but for example, it is 0 μg or more. Specifically, the phosphorus atom content per gram of the optical styrene resin composition is, for example, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 50, 60, 70, 80, 90, and 100 μg, and may be within the range of any two of the values exemplified here. By setting it within this range, the optical styrene resin composition has excellent light stability. The phosphorus atom content can be adjusted, for example, by the amount of phosphorus-based antioxidant (C-1) added.

The optical styrene resin composition preferably satisfies the following formula (1) when the content of styrene monomers per 1 g of the optical styrene resin composition is M μg, the content of styrene monomer linear dimers is D μg, the content of styrene monomer linear trimers is T μg, and the content of phosphorus atoms is P μg. "(M + D + T) × P" is more preferably 15,000 or less, and even more preferably 10,000 or less. By keeping it within this range, the optical styrene resin composition has excellent light stability.
(M+D+T)×P≦20000 (1)

The method for measuring the content of styrene monomers, linear dimers of styrene monomers, and linear trimers of styrene monomers in an optical styrene resin composition is not particularly limited, but can be measured, for example, using a gas chromatograph.

In one example, when using a synthesized styrene resin (A), the composition is prepared by accurately weighing the styrene resin (A) before preparation, dissolving it in tetrahydrofuran (THF) together with an internal standard (e.g., p-diethylbenzene), measuring the styrene monomer content using a capillary gas chromatograph, calculating the styrene monomer content relative to the styrene resin (A), and converting this to the content (μg) per 1 g of the optical styrene resin composition. A calibration curve for styrene monomers is prepared in advance and used for quantification.

In another example, the weight of an optical styrene-based resin composition is accurately measured, dissolved in tetrahydrofuran (THF) together with an internal standard (e.g., p-diethylbenzene), and the styrene monomer content is measured using a capillary gas chromatograph. A calibration curve for styrene monomers is prepared in advance and used for quantification.

For example, when using a synthesized styrene-based resin (A), the content of styrene monomer linear dimers and styrene monomer linear trimers in the styrene-based resin (A) before composition preparation can be measured by preparing the following measurement solution. The measurement solution is prepared by adding THF to the styrene-based resin (A), sonicating to extract the material, then adding hexane to precipitate the polymer, allowing it to stand, and then concentrating the supernatant. The measurement solution is then measured using a capillary gas chromatograph to calculate the content of styrene monomers in the styrene-based resin (A), and this is converted to the content (μg) per 1 g of the optical styrene-based resin composition using this solution. Note that styrene monomer linear dimers and styrene monomer linear trimers can be synthesized or obtained commercially, and calibration curves for these can be prepared in advance and used for quantification.

In another example, the content of styrene monomer linear dimers and styrene monomer linear trimers in an optical styrene resin composition can be measured by preparing the following measuring solution. The measuring solution is prepared by adding THF to the optical styrene resin composition, sonicating it to extract the material, then adding hexane to precipitate the polymer, allowing it to stand, and finally concentrating the supernatant. The measuring solution is then measured using a capillary gas chromatograph. Note that styrene monomer linear dimers and styrene monomer linear trimers can be synthesized or obtained commercially, and calibration curves for them can be prepared in advance and used for quantification.

Here, styrene monomer linear dimers and styrene monomer linear trimers refer to dimerized and trimerized products of styrene monomers. These dimerized and trimerized products originate from styrene monomers used in the synthesis of styrene resin (A), for example (by-products, etc.). Styrene monomer dimerized and trimerized products can be formed by bonding in a linear manner (linear dimer/linear trimer) or by bonding in a non-linear manner (e.g., cyclic) (non-linear dimer/non-linear trimer). In this invention, the content of linear styrene monomer linear dimers and styrene monomer linear trimers is specified.

Furthermore, when multiple types of styrene monomers are used, styrene monomer linear dimers and styrene monomer linear trimers may include not only those formed by the dimerization or trimmerization of the same type of styrene monomer, but also those formed by the bonding of two or three different types of styrene monomers.

In the synthesis of styrene-based resin (A), when styrene is used as the styrene monomer, 2,4-diphenyl-1-butene can be produced as the linear dimer of the styrene monomer, and 2,4,6-triphenyl-1-hexene can be produced as the linear trimer of the styrene monomer. In one embodiment in which styrene is used as the styrene monomer, the optical styrene-based resin composition preferably has a styrene content of 1000 μg or less per 1 g of the optical styrene-based resin composition, and the total content of 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene is 10 to 500 μg. In one embodiment in which styrene is used as the styrene monomer, the above-mentioned numerical ranges for the content of styrene monomer, the total content of styrene monomer linear dimers and styrene monomer linear trimers, their respective contents, and the relationship in formula (1) can be preferred numerical ranges for styrene, 2,4-diphenyl-1-butene, and 2,4,6-triphenyl-1-hexene.

The phosphorus atom content can be calculated, for example, from the amount of phosphorus-containing additives (such as phosphorus-based antioxidants) added to the optical styrene resin composition. Alternatively, the phosphorus atom content may be obtained by elemental analysis or ICP-AES (ICP emission spectrometry) of the optical styrene resin composition, or by other analytical methods.

<Other ingredients>
The t-butylcatechol (TBC) content in the optical styrene resin composition is preferably 10 ppm or less, and more preferably 5 ppm or less. This range allows for the production of a light guide plate with excellent hue and transmittance. Specifically, the TBC content may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 ppm, and may also be within the range of any two of the values exemplified here.

The 6-tert-butyl-2,4-xylenol (TBX) content in the optical styrene resin composition is preferably 10 ppm or less, and more preferably 5 ppm or less. This range allows for the production of a light guide plate with excellent hue and transmittance. Specifically, the TBX content may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 ppm, and may also be within the range of any two of the values exemplified here.

The optical styrene resin composition may contain, to the extent that it does not impair the properties of the present invention, release agents such as sulfur-based antioxidants, lactone-based antioxidants, ultraviolet absorbers, antistatic agents, hydrophilic additives, liquid paraffin (mineral oil), polyethylene wax, microcrystalline wax, bluing agents, higher fatty acids such as lauric acid, myristic acid, palmitic acid, and stearic acid, higher fatty acid amides such as stearic acid amide, erucic acid amide, and ethylenebis-stearic acid amide, higher fatty acid glycerides such as lauric acid monoglyceride, palmitic acid monoglyceride, stearic acid monoglyceride, and behenic acid monoglyceride, and higher alcohols such as myristyl alcohol, cetyl alcohol, and stearyl alcohol.

<Properties of styrene-based resin compositions for optical applications>
The melt mass flow rate (MFR) of the optical styrene resin composition under conditions of 200°C and a 49N load is preferably 0.5 to 5.0 g/10 min, and more preferably 1.0 to 4.0 g/10 min. If the MFR is less than 0.5 g/10 min, the molding stability decreases, and if the MFR exceeds 5.0 g/10 min, the strength becomes insufficient. Specifically, the MFR may be, for example, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, or 5.0 g/10 min, and may also be within the range of any two of the values exemplified here.

The Vicat softening temperature of the optical styrene resin composition is preferably 95 to 104°C, and more preferably 100 to 104°C. If the Vicat softening temperature is below 95°C, the heat resistance will be insufficient, and the light guide plate may deform depending on the usage environment. Specifically, the Vicat softening temperature may be, for example, 95, 96, 97, 98, 99, 100, 101, 102, 103, or 104°C, and may also be within the range of any two of the values exemplified here.

The optical styrene resin composition has an average transmittance of 85% or more, and more preferably 86% or more, at a wavelength of 380 to 780 nm with an optical path length of 115 mm in the molded article.

The optical styrene resin composition has a YI value of 6.0 or less, and more preferably 4.0 or less, at an optical path length of 115 mm in the molded body.

When an optical styrene resin composition is stored for 500 hours under conditions of a temperature of 60°C and a relative humidity of 90%, the change in the length of the long side before and after storage is preferably 0.15% or less, and more preferably less than 0.10%, as calculated by the following formula.

The styrene-based resin composition for optical applications preferably requires 150 hours or more, more preferably 400 hours or more, and even more preferably 600 hours or more, for the molded article's yellowness YI to exceed 20 after blue LD irradiation. Detailed conditions for blue LD irradiation will be described in the examples below.

<Method for producing optical styrene resin composition>
Known styrene polymerization methods include bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization is preferable. Examples of solvents that can be used include alkylbenzenes such as benzene, toluene, ethylbenzene, and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

During the polymerization of the styrene-based resin (A), polymerization initiators, chain transfer agents, crosslinking agents, and other polymerization aids can be used as needed. As polymerization initiators, radical polymerization initiators are preferred, including well-known and conventional peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di-t-butylperoxycyclohexyl)propane, and 1,1-di(t-amylperoxy)cyclohexane; hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide; alkyl peroxides such as t-amylperoxyisononanoate; and dialkyl peroxides such as t-butylcumyl peroxide, di-t-butyl peroxide, dicumyl peroxide, and di-t-hexyl peroxide. Examples include peroxides, peroxyesters such as t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butyl peroxyisopropyl monocarbonate, peroxycarbonates such as t-butyl peroxyisopropyl carbonate and polyethertetrakis(t-butyl peroxycarbonate), and N,N'-azobis(cyclohexane-1-carbonitride), N,N'-azobis(2-methylbutyronitrile), N,N'-azobis(2,4-dimethylvaleronitrile), and N,N'-azobis[2-(hydroxymethyl)propionitrile]. One or more of these can be used in combination. Examples of chain transfer agents include aliphatic mercaptans such as n-dodecyl mercaptan and tert-dodecyl mercaptan, aromatic mercaptans, thiocarboxylic acids such as thioglycolic acid and mercaptopropionic acid, polyhydric alcohols such as ethylene glycol, tetraethylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and sorbitol, polyfunctional mercaptans obtained by esterifying the hydroxyl group of polyhydric alcohols with thioglycolic acid or mercaptopropionic acid, pentaphenylethane, α-methylstyrene dimer, and terpinolene. Among these, aliphatic mercaptans, aromatic mercaptans, thiocarboxylic acids, and polyfunctional mercaptans are preferred because their molecular weight can be easily adjusted.

In the case of continuous polymerization, styrene-based resin (A) can be produced by a method comprising a polymerization step, a defoliation step, and a granulation step.

First, in the polymerization process, known fully mixed stirring tanks or tower reactors are used to control the polymerization reaction by adjusting the polymerization temperature and other factors to achieve the target molecular weight, molecular weight distribution, and reaction conversion rate.

The polymerization solution containing the polymer that has exited the polymerization process is transferred to the defoliation process, where unreacted monomers and polymerization solvent are removed. The defoliation process consists of a vacuum defoliation tank with a heater, etc. Alternatively, the defoliation process may be carried out by introducing the polymer-containing solution, continuously extracted from the reactor, into a vacuum defoliation tank with a preheater, consisting of two stages in series. In the first stage defoliation tank, for example, the temperature can be set to 160 to 200°C and the pressure to 0.8 to 1.2 kPa. In the second stage defoliation tank, for example, the temperature can be set to 201 to 250°C and the pressure to 0.5 to 0.9 kPa. The molten polymer that has exited the defoliation process is transferred to the granulation process. In the granulation process, the molten resin is extruded in strand form from a porous die and processed into pellet form using a cold-cut method, an air-hot-cut method, or an underwater-hot-cut method. Furthermore, it is preferable not to perform defoliation or the addition of additives while kneading with an extruder, in order to suppress the generation of dimerized and trimerized products (depolymerization due to thermal history).

The optical styrene resin composition may optionally contain a hindered amine light stabilizer (B), a phosphorus-based antioxidant (C-1), and a phenol-based antioxidant (C-2) as needed. The hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenol-based antioxidant (C-2) may be added to the raw material solution before polymerization of the styrene resin (A), or they may be mixed in a static mixing device after polymerization of the styrene resin (A).

The content of t-butylcatechol or 6-tert-butyl-2,4-xylenol in the optical styrene resin composition can be adjusted at the start of polymerization of the styrene resin (A) and in subsequent defoliation steps.

2. Molded Body and Light Guide Plate The above optical styrene resin composition can be used for applications that transmit light from an LED light source having maximum radiant intensity in the wavelength range of 400 nm to 500 nm. A molded body according to one embodiment of the present invention is a molded body composed of the above optical styrene resin composition, which can be obtained by molding the above optical styrene resin composition. A light guide plate according to one embodiment of the present invention is a light guide plate comprising a molded body composed of the above optical styrene resin composition, which can be obtained by molding the above optical styrene resin composition. The light guide plate is a light guide plate that can be used in an edge-lit surface light source unit.

<Shape of the light guide plate>
The light guide plate may have an uneven surface. More specifically, the surface of the light guide plate may have a plurality of lenticular and/or prism-shaped protrusions. Preferably, the protrusions are provided on at least one surface of the light guide plate, and particularly on the front surface (light-emitting surface) of the light guide plate. They may also be provided on other surfaces if necessary, but it is more preferable that they are provided only on the front surface (light-emitting surface) of the light guide plate.

Here, a lenticular convex portion is an arc-shaped convex portion, with a cross-sectional edge shape that is an arc-shaped projection. A prism-shaped portion is an arc-shaped convex portion, with a cross-sectional edge shape that is a triangular peak. Furthermore, multiple convex portions can be formed parallel to each other. Also, the convex portions can be formed integrally with the light guide plate.

The thickness of the light guide plate is 0.2 to 3.0 mm, preferably 0.3 to 2.5 mm, and more preferably 0.4 to 2.4 mm. Within this range, it is easy to manufacture a light guide plate with excellent moldability, such as excellent extrusion stability, and strength when molding an optical styrene-based resin composition.

<Optical properties>
The average transmittance of the light guide plate at a wavelength of 380 to 780 nm with an optical path length of 115 mm is preferably 85% or higher, and more preferably 86% or higher.

The YI value at an optical path length of 115 mm of the light guide plate is preferably 6.0 or less, and more preferably 4.0 or less.

<Manufacturing method for light guide plates>
A light guide plate according to one embodiment of the present invention is obtained by molding the above-mentioned optical styrene-based resin composition. Known methods such as sheet extrusion molding, injection molding, and compression molding can be used as molding methods, but continuous sheet extrusion molding with a surface shape transfer mold is preferred in terms of productivity and ease of scaling up molded products. An example of such sheet extrusion molding is a continuous sheet extrusion molding method that includes an extrusion step in which resin is supplied to a feed block in a heated and molten state and a sheet is continuously extruded from a die, a pressing step in which the resin sheet is sandwiched between a pressure roll and a cooling roll, and a conveying step in which the resin sheet is conveyed while being in close contact with the cooling roll after the pressing step, and a transfer mold is provided on the surface of the cooling roll. By changing the shape of the transfer mold, any uneven shape can be transferred to the sheet surface.

Furthermore, the light guide plate may have an uneven surface on its front (light-emitting surface), and its back surface may be treated with a reflective coating to diffusely reflect light. Examples of reflective coatings include silk screen printing, inkjet printing, and laser irradiation to create dot-shaped irregularities. For printing the dot pattern, an ink containing light-diffusing fine particles can be used. In other words, the light guide plate may comprise a light guide layer (light guide section) made from the above-mentioned optical styrene-based resin composition, and a reflective coating layer (reflective coating section) for reflection.

3. Edge-lit surface light source unit An edge-lit surface light source unit according to one embodiment of the present invention is an edge-lit surface light source unit having the above-mentioned light guide plate and a light source that supplies LED light to the end face of the light guide plate. The edge-lit surface light source unit is suitably used as a surface light source device for liquid crystal display devices.

The present invention will be described in more detail below with reference to examples. These examples are illustrative and do not limit the scope of the present invention.

1. Production of styrene-based resin composition for optical applications [Example 1]
A polymerization process was constructed by connecting a first reactor, a fully mixed stirred tank, and a second reactor, a plug-flow type reactor with a static mixer, in series, to produce a styrene-based resin (A). The capacity of each reactor was 30 liters for the first reactor and 12 liters for the second reactor. As shown in Table 1, with a raw material composition of 51% by mass of styrene, 39% by mass of methyl methacrylate, and 10% by mass of ethylbenzene, the addition concentrations of 150 ppm of t-butyl peroxyisopropyl monocarbonate (manufactured by NOF Corporation: Perbutyl I) as a polymerization initiator and 500 ppm of n-dodecyl mercaptan (manufactured by Arkema Corporation) as a chain transfer agent were adjusted at the inlet of the first reactor (both concentrations are based on mass relative to the raw material feed (total raw material monomers) [*1 in Table 1]). The raw material solution was then continuously supplied at 8.0 kg/h to the first reactor, which was set to 128°C. Furthermore, the resulting polymerization solution was continuously supplied to the second reactor to complete the polymerization. The monomer polymerization rate at this time was 70%. In the second reactor, a temperature gradient was created along the flow direction, and the temperature was adjusted to 130°C in the middle section and 145°C at the outlet section.
Next, the polymer-containing solution continuously extracted from the second reactor was introduced into a vacuum defloration tank with a preheater, consisting of two stages in series. The temperature and pressure were adjusted to those shown in Table 2, and unreacted monomers and ethylbenzene were separated. Various additives were melted and added to the resulting molten polymer in the amounts shown in Table 2. The mixture was then extruded into strands through a porous die via an SMX (static mixer), and the strands were cooled and cut using a cold-cut method to form pellets.

<Amount of monomers in optical styrene-based resin composition>
The amount of styrene monomer (styrene) in styrene resin (A) was measured by accurately weighing 0.2 g of styrene resin (A), which was separated before the melting and addition of various additives, dissolving it in 10 mL of tetrahydrofuran (THF) containing p-diethylbenzene as an internal standard, and measuring it using a capillary gas chromatograph under the following conditions. In the table, the measurement results are shown converted to content (μg) per 1 g of optical styrene resin composition.
Capillary gas chromatograph: GC-4000 (manufactured by GL Sciences Co., Ltd.)
Column: InertCap WAX, manufactured by GS Science Co., Ltd., inner diameter 0.25 mm, length 30 m, film thickness 50 μm
Injection temperature: 180°C
Column temperature: 60°C to 170°C
Detector temperature: 210°C
Split ratio: 5/1

<Content of dimers and trimers in optical styrene resin compositions>
The content of styrene-based linear dimer (2,4-diphenyl-1-butene) and styrene-based linear trimer (2,4,6-triphenyl-1-hexene) of the styrene monomer (styrene) in styrene-based resin (A) was measured under the following conditions and procedure.
Sample preparation: 0.1 g of styrene resin (A) was mixed with 5 mL of THF and extracted by sonication. Then, hexane was added to bring the solution volume to 50 mL to precipitate the polymer components. After standing, the supernatant (total volume) was concentrated to 2 mL and used as the measurement solution. In Tables 2 to 4, the measurement results are shown converted to content (μg) per 1 g of optical styrene resin composition.
Measurement conditions: Gas chromatograph: JEOL K9 (JEOL Ltd.)
Column: ZB-5MS 0.25 mm x 30 m, film thickness 0.25 μm
Injection temperature: 200°C
Column temperature: 40-320°C
Detector temperature: 300°C
Split ratio: 10/1
Ionization method: EI
Mass range: m/z=29-600
Carrier gas: Nitrogen. Additionally, 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene were purchased from Fujifilm Wako Pure Chemical Corporation, and a calibration curve was created for quantitative analysis.

<Meltmass Flow Rate (MFR)>
The melt mass flow rate of the optical styrene resin composition was measured in accordance with JIS K 7210 under conditions of 200°C and a 49N load.

<Vicat softening temperature>
The Vicat softening temperature of the optical styrene resin composition was measured according to JIS K 7206, with a heating rate of 50°C/hr and a test load of 50 N.

<Molecular weight>
The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of styrene resin (A) were measured using gel permeation chromatography (GPC) under the following conditions.
GPC model: Showa Denko Corporation Shodex GPC-101
Column: PLgel 10 μm MIXED-B, manufactured by Polymer Laboratories, Inc.
Mobile phase: Tetrahydrofuran; Sample concentration: 0.2% by mass
Temperature: Oven 40°C, Inlet 35°C, Detector 35°C
Detector: Differential refractometer. Molecular weight was calculated by determining the molecular weight at each elution time from the elution curve of monodisperse polystyrene, and then calculating the molecular weight in polystyrene equivalent.

Below, a plate-shaped test piece 1 was prepared as a molded body simulating a light guide plate, and the properties of the molded body were evaluated.

<Evaluation of optical properties of resin compositions>
Using the obtained styrene-based resin composition pellets, injection molding was performed at a cylinder temperature of 230°C and a mold temperature of 60°C. As shown in Figure 1, a mold polished so that the end face 3 was mirror-finished was used to form a molded body (plate-shaped test piece 1) measuring 115 mm × 80 mm × 3 mm (length × width × thickness) (the opposite sides of each face shown as end face 3 were also mirror-finished). Using a UV-Vis spectrophotometer V-670 manufactured by JASCO Corporation, the spectral transmittance from wavelengths of 350 nm to 800 nm was measured with incident light of size 20 × 1.6 mm and a divergence angle of 0°, with an optical path length of 115 mm. The YI value at a field of view of 2° in the C light source was calculated according to JIS K7105. The average transmittance shown in Tables 2 to 4 refers to the average transmittance from wavelengths of 380 nm to 780 nm.

<Dimensional Stability>
Plate-shaped test specimen 1 was stored for 500 hours under conditions of a temperature of 60°C and a relative humidity of 90%, and the change in the dimensions of the long side before and after storage was measured. The deformation rate was calculated using the following formula.
Deformation rate = ((Longest side length after storage) - (Longest side length before storage)) ÷ (Longest side length before storage) × 100 (%)
The dimensional stability (moisture-induced deformation) of the molded articles was evaluated by assigning a ○ (circle) to those with a change rate of less than 0.10%, a △ (triangle) to those between 0.10% and 0.15%, and a × (cross) to those with a change rate greater than 0.15%.

<Evaluation of Blue LD Durability of Resin Compositions>
The irradiated area was set near the center of surface 5 of the plate-shaped test specimen 1. A PLS-1000S optical fiber (450 ± 10 nm) from Presize Gauge Co., Ltd. was placed 0.5 mm above the irradiated area, and the plate-shaped test specimen 1 was irradiated with a blue LD at room temperature. The illuminance was measured using an illuminometer (Hamamatsu Photonics K.K. sensor head H12684-385, controller C12144), and the illuminance was found to be 12 W/ ^cm² . Subsequently, the plate-shaped test specimen 1 was removed every 50 hours, and the yellowness YI of the irradiated area was measured using a COLOR-7e2 color difference meter (manufactured by Kurabo Industries Ltd.). The time at which the value exceeded 20 was recorded in the table. A specimen was considered acceptable if the time at which the yellowness YI exceeded 20 was more than 100 hours.

[Examples 2-22 and Comparative Examples 1-4]
An optical styrene-based resin composition and molded article (plate-shaped test piece 1) were manufactured in the same manner as in Example 1, except that the composition of the raw material solution and polymerization conditions were changed as shown in Table 1, and the formulations of the styrene-based resin (A), resin hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenol-based antioxidant (C-2) were changed as shown in Tables 2 to 4. The results of various measurements and evaluations are shown in Tables 2 to 4. In the tables, "ND" indicates that no phosphorus atoms were detected.

Furthermore, the hindered amine light stabilizer (B), phosphorus-based antioxidant (C-1), and phenol-based antioxidant (C-2) in Tables 2 to 4 are as follows:

(Hindered amine light stabilizer (B))
944: Polycondensate of 2,4-dichloro-6-(1,1,3,3-tetramethylbutylamino) and 1,3,5-triazine/N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine (BASF Chimassorb 944FDL)
292: A mixture of 25% methyl(1,2,2,6,6-pentamethylpiperidine-4-yl) sebacate and 75% bis(1,2,2,6,6-pentamethylpiperidine-4-yl) sebacate (BASF TINUVIN 292).

(Phosphorus-based antioxidant (C-1))
168: Tris(2,4-di-tert-butylphenyl) phosphite (BASF Irgafos 168)
HP-10: 2,2'-methylenebis(4,6-di-tert-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus (ADKSTAB HP-10, manufactured by ADEKA Corporation)
PEP-36: 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (ADEKA Corporation, ADEKA Stab PEP-36)

(Phenol-based antioxidant (C-2))
1076: Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (BASF Irganox 1076)

Examples 1 to 22 exhibited good transparency (average transmittance), hue (YI value), and dimensional stability, as well as excellent LD durability.

1: Molded product 3: End surface (mirror surface)
5: Face

Claims (8)

A styrene-based resin composition for optical applications, comprising a styrene-based resin,
Per 1 g of the aforementioned optical styrene-based resin composition,
The styrene monomer content is 1000 μg or less.
The total content of styrene monomer linear dimers and styrene monomer linear trimers is 10 to 500 μg.
The styrene-based resin is a copolymer comprising 95 to 20% by mass of styrene monomer units and 5 to 80% by mass of (meth)acrylic acid ester monomer units.
The aforementioned styrene-based resin contains 0.001 to 0.5 parts by mass of a hindered amine light stabilizer per 100 parts by mass of the styrene-based resin.
A styrene-based resin composition for optical applications. The optical styrene-based resin composition according to claim 1, wherein the phosphorus atom content is 50 μg or less per 1 g of the optical styrene-based resin composition. When the content of the styrene monomer is Mμg, the content of the styrene monomer linear dimer is Dμg, the content of the styrene monomer linear trimer is Tμg, and the content of the phosphorus atom is Pμg per 1g of the optical styrene resin composition,
An optical styrene-based resin composition according to claim 1, satisfying the following formula (1).
(M+D+T)×P≦20000 (1) The optical styrene-based resin composition according to claim 1, wherein the hindered amine light stabilizer is an N-R type hindered amine light stabilizer. A molded article comprising an optical styrene-based resin composition according to any one of claims 1 to 4 . A light guide plate comprising the molded body according to claim 5 . An edge-lit surface light source unit comprising a light guide plate according to claim 6 and a light source that supplies LED light to the end face of the light guide plate. A method for producing a styrene-based resin composition according to any one of claims 1 to 4,
The manufacturing method includes a defoliation step to remove volatile components from the polymer solution after polymerization, and the defoliation step is
The temperature in the first stage of the first defoliation tank is set to 160-200°C and the pressure to 0.8-1.2 kPa.
The process is carried out in two stages, with the temperature in the second defoliation tank set to 201-250°C and the pressure to 0.5-0.9 kPa, and
This process is not carried out while the mixture is being kneaded in an extruder.
A method for producing an optical styrene-based resin composition.